The present invention relates to a method and a system for compensating a detected position detected by a resolver.
Japanese Patent No. 2541169 and Japanese Patent Laid-open Publication No. 7-336979 show conventional techniques for compensating a position detected by a resolver. These prior arts compensate the detected position by performing a static error compensation by which a static error defined as an error from a real position when a rotor of the resolver is at rest, is compensated.
With the conventional technique of Japanese Patent No. 2541169 in particular, as claimed in its claims, the position compensation procedure involves differentiating a detected position signal from the resolver when a motor is driven at a constant speed, calculating from the differentiated signal position compensation data corresponding to rotational positions of the rotor, and storing the calculated result in memory. When a motor is controlled, the position compensation data corresponding to the detected position signal from the resolver is read out from the memory to perform a necessary compensation and the compensated data is used as a position signal. This conventional technique does not perform in advance the static error compensation on the detected position signal which is to be compensated. Thus, the position compensation data obtained by driving the motor at a constant speed is intended for compensating the static error. This is obvious from the following descriptions in the reference cited above. That is, at lines 18–21 in fourth column on page 2 the above patent reads that “speed ripples of large magnitudes are those that appear during one rotation of the rotor as many as the number of pole pairs”, provided that a frequency characteristic for the speed control is sufficiently smaller than the pole-pair-number ripples during a constant rotation. The patent also reads at lines 48–49 in third column on page 2 that “in the case of a multi-pole resolver, this compensation needs only to be repeated the same number of times during one machine angle rotation as the number of pole pairs”. These descriptions clearly indicate that the errors (ripples) to be compensated are those ripples that appear during one rotation of the rotor as many as the number of pole pairs, i.e., the ripples are static errors.
Further, the Japanese Patent Laid-open Publication No. 7-336979 describes a method of improving errors that uses a compensated speed detection signal and a compensated detected position signal both obtained by compensating the static errors to estimate a delay in signal processing and a position for interpolating between data samplings.
Conventionally only the effect of the static errors of the resolver has been considered and the object to be compensated by the conventional techniques is only the static errors. This is because the rotational speed of conventional motors using the resolver is mostly lower than 5,000 min−1 and in this range of rotational speed no problem arises if only the static errors are compensated. According to the conventional wisdom in the art the resolver needs only to have its static errors compensated. If, for example, the motor rotational speed is about 4,500 min−1, errors pose no particular problem. However, when the rotational speed of the rotor of the resolver exceeds 10,000 min−1, it is found that errors (dynamic errors) occur despite the fact that the static errors of the output of the resolver are compensated. When the rotational speed of the rotor of the resolver increases to 20,000 or 30,000 min−1 for example, the dynamic errors become large, thereby greatly degrading the position detection accuracy. This problem has not been known because the conventional resolver has not been used for position detection at high rotational speeds.
An object of this invention is to provide a resolver detected position compensation method and system which can enhance a position detection accuracy by performing a second compensation on a compensated detected position which has undergone a static error compensation.
Another object of this invention is to provide a resolver detected position compensation method and system which can enhance a detection accuracy of the resolver by eliminating a dynamic error signal which includes twice as many ripples, which appear during one rotation of the rotor running at high speed, as the number of pole pairs of the resolver.
Still another object of this invention is to provide a resolver detected position compensation method and system which can easily and reliably compensate dynamic errors that vary with a change in rotational speed of the resolver rotor.